Domain Wall Relaxation Frequency Research Articles

Amorphous Fe72Cu1V4Si15B8 ribbon as magneto-impedance sensing element

?agneto-impedance (MI) effect in the Fe72Cu1V4Si15B8 amorphous ribbon obtained by melt spinning method has been studied. The aim of study was the characterisation of this ribbon in as-cast state in terms of its application as a MI sensor. The experiments on MI elements were performed in the frequency range from 30 kHz to 300 MHz and maximum external magnetic field up to 28.6 kA/m. Maximum observed MI-ratio (?Z = Z(0) - Z(Hmax), Hmax = 28.6 kA/m) has amounted to ?Z/Z(Hmax) = 173% at a frequency of 20.46 MHz. The MI curve measured up to 20 MHz shows some shoulder indicating the growth of rotational contribution of magnetization that appears above the domain wall relaxation frequency. The MI profile at frequencies higher than 30 MHz, exhibits a clear peak positioned at transverse anisotropy field Hk, suggesting domination of rotation magnetization in transverse permeability. The linearity in the range up to 5 kA/m with sensitivity of about 11 %/kA/m was observed.

Structural and magnetic properties of Mg substituted NiCuZn Nano Ferrites

The present paper examines the effect of magnesium substitution on structural and magnetic properties of NiCuZn nano ferrites synthesised by sol-gel method. The prepared samples were characterised by using X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Field Emission Scanning Electron Microscopy (FE-SEM) and Vibration sample magnetometer (VSM) techniques. The phase identification, unit cell parameter and crystallite size was determined using XRD analysis. The lattice constant reduced with increasing Mg content. Room temperature saturation magnetisation and coercivity showed reverse trend with increasing Mg content. Curie temperature (Tc) obtained from the thermo magnetic curves increases with Mg concentration. The initial permeability (μi) decreased with increasing Mg content. This is due to reduced magnetisation, grain size and increased magneto-crystalline anisotropy constant. Simultaneously, there is an upward shift of domain wall relaxation frequency with increasing Mg content. Also the permeability is observed to be constant up to 30MHz frequency range showing compositional stability and quality of the material. The prepared samples were suitable for applications in Multilayer Chip Inductors due to their invariable permeability up to 30MHz frequency and high thermal stability along with low sintering temperature.

Investigation of structural and magnetic properties of polycrystalline Ni 0.50Zn 0.50− xMg xFe 2O 4 spinel ferrites

The structural and magnetic properties of Mg substituted Ni 0.50Zn 0.50− x Mg x Fe 2O 4 (where x = 0.0, 0.10, 0.20, 0.30, 0.40 and 0.50) sintered at various temperatures have been studied thoroughly. X-ray diffraction patterns of the samples showed single-phase cubic spinel structure without any detectable impurity phases. The lattice parameter decreases linearly with increase of Mg contents obeying Vegard's law. The bulk density, average grain size and initial permeability, μ i ′ , decrease with increasing Mg substitution but increase with increasing sintering temperature for a particular composition. The highest initial permeability and quality factor, Q, are obtained for the Ni 0.50Zn 0.50Fe 2O 4 sintered at 1350 and 1250 °C, respectively. Domain wall relaxation frequency, f r, and Néel temperature, T N, are found to increase with Mg substitution. It is observed that when Zn is completely substituted by Mg in Ni 0.50Zn 0.50− x Mg x Fe 2O 4, the T N is increased by 106% and f r by 178%. On the other hand, μ i ′ decreases by 86%. It is observed that all samples are in ferrimagnetic state at room temperature. The number of Bohr magneton, n( μ B), decreases with increasing Mg substitution which is explained by probable cation distribution in the spinel crystal structure. Possible explanation for the observed features of microstructure, initial permeability, DC magnetization and Néel temperature of the studied samples are discussed.

Domain wall relaxation frequency and magnetocrystalline anisotropy in Co- and Fe-based nanostructured alloys

The magnetic behaviour and the frequency dependence of the initial complex permeability are analysed in very soft ferromagnetic Co- and Fe-based nanostructured alloys obtained by thermal treatments of amorphous ribbons. The spectra of the real and imaginary parts of the permeability show the typical features of domain wall relaxation and are characterized by a continuous distribution of relaxation times. In the framework of the random anisotropy model, the spread in the values of the relaxation frequency reflects a dispersion of the effective anisotropy constants and, in turn, a nonuniform distribution of the grain diameters. The results well agree with those deduced by the distribution function of the anisotropy fields and by the scanning and/or transmission electron microscopy analysis.

Frequency behaviour of Zn–Mn ferrites nanoparticles obtained by high-energy ball milling

Zinc–manganese spinel ferrites have been obtained by high-energy ball milling from precursors (1) oxides and carbonates and (2) acid oxides and hydroxides. Results reveal that the use of one or another precursor leads to final products with different structural and magnetic characteristics. Measurements of the domain wall relaxation frequency exhibited differences depending on the type of precursor. These results are interpreted in terms of the variations in the magnetocrystalline anisotropy between the samples.

Magnetization dynamics of pinned domain walls in partially crystallized ribbons

The frequency dependence of the permeability of Co- and Fe-rich amorphous ribbons (Vitrovac 6025(R) and Metglas(R) 2605 SC, respectively), submitted to a variety of thermal treatments involving different degrees of crystallization, was measured in the 5 Hz-13 MHz frequency range. The quasi-static initial permeability, /spl mu//sub i/, and the domain wall relaxation frequency, f/sub x/, exhibited an inverse relationship, /spl mu//sub i//spl middot/f/sub x/=constant. These results are interpreted in terms of variations in the average distance between pinning points of domain walls, and the effects of such variations on the vibrational properties of pinned domain walls.

Thickness dependence of dielectric losses in TGSe

Abstract Dielectric losses in TGSe were measured in the frequency range from 20 Hz to 1 MHz for various thicknesses. Domain wall relaxation frequencies decrease with increasing sample thickness. Temperature dependence of the domain wall relaxation frequency was also analysed.

Domain wall relaxation frequency and magnetocrystalline anisotropy constant in NiZn ferrites

The frequency behavior of polycrystalline ferrites with composition Zn 0.64Ni 0.36Fe 2O 4 was investigated in the 100 Hz to 13 MHz frequency and 200–400 K temperature ranges. A comparison of the thermal behavior of the domain wall relaxation frequency with the magnetocrystalline anisotropy constant exhibited a linear relationship. These results are interpreted in terms of the restoring force factor for wall bulging. We explore the possibility of using frequency measurements to investigate the anisotropy constant in polycrystalline samples.

Effects of tensile stress on the domain wall dynamics of Co-based amorphous ferromagnetic wires

Complex permeability measurements were performed on Co72.5B15Si12.5 amorphous wires, as a function of tensile stress, at room temperature and in the frequency range 5 Hz – 13 MHz. Rotational and initial permeabilities showed a decrease as tensile stress increased. The domain wall relaxation frequency exhibited a linear behavior as stress increased. These results are interpreted in terms of the magnetoelastic contribution to anisotropy.

Effects of nanocrystallization upon the soft magnetic properties of Co-based amorphous alloys

Amorphous samples of Vitrovac(R) 6025 metallic alloys were nanocrystallized by thermal annealing at temperatures in the range 576–716 K, well below the crystallization temperature (831 K, as obtained by differential scanning calorimetry at 20 K/min) and times in the range 10–90 min. Initial magnetic permeability exhibited a maximum of ∼109 000 (from ∼20 000 for the as-quenched state) for annealing times of ∼15 min, and then a decrease toward a plateau value (30 000–40 000) for longer times. Domain wall relaxation frequency showed the opposite behavior, a minimum of ∼9 kHz (from 40 kHz for the as-quenched value) for the permeability maximum, and then a stabilization at ∼15 kHz. Transmission electron microscopy observations confirmed that for annealing times up to 60 min., crystallite size is smaller than 30 nm. Permeability and relaxation frequency results are interpreted in terms of the dependence of wall bulging on anisotropy and free-wall surface area between pinning sites.

Effects of crystallization on the magnetization dynamics of Vitrovac amorphous ribbons

Co-based soft ferromagnetic amorphous ribbons (Vitrovac R 6025) were crystallized by annealing at various temperatures (100–250 K below the crystallization temperature, 831 K) for times ranging from 1 to 18 h. The initial permeability was determined from complex permeability plots in the frequency range 5 Hz–13 MHz. A decrease in initial permeability μ i as a function of annealing time was observed for all annealing temperatures. This decrease was sharper at higher temperatures. The domain wall relaxation frequency ƒ 0 exhibited inverse behaviour; the product μ i ƒ 0 was practically constant for all the experiments. It is shown that these results can be interpreted on the basis of a reversible magnetization mechanism of domain wall bowing, and that the decrease in permeability results from increased wall pinning due to crystallization.

Domain wall dynamics and short-range order in ferromagnetic amorphous ribbons

The initial magnetic permeability, μ 0, of Vitrovac 6025® amorphous ribbons has been investigated as a function of time at temperatures 296–423 K, in the frequency range 100 Hz-13 MHz. The domain structure is unperturbed during the experiments, since only fields below the critical field value are applied. Both the domain wall relaxation frequency, f 0, and the initial permeability show a power-law dependence upon time; they can be related by μ 0 α f 0 = constant in this temperature range. These results can be interpreted on the basis of domain wall pinning and its dependence on short-range pair ordering on wall sites.

Effects of thermal annealing on the magnetization dynamics of vitrovac amorphous ribbons

The effects of thermal annealing on the frequency behavior of the initial permeability, μ0, of Vitrovac(r) 6025 amorphous ribbons have been investigated. For annealing temperatures above the Curie point, Tc, μ0 shows a significant increase (from 13 760 to 39 600) as compared with the as-quenched sample; for annealing temperatures below Tc (‘‘aging’’), μ0 decreases (from 13 760 to 7700). The domain wall relaxation frequency exhibited the opposite behavior: a decrease with annealing at T≳Tc (from 69 to 18 kHz) and an increase with aging (from 69 to 127 kHz). The frequency behavior can be modeled by means of a simple, parallel RL circuit, where the inductance value is proportional to the initial permeability, and the equivalent resistance value, which is inversely related to the damping parameter, is the same for all the samples. These results can be interpreted on the basis of a variation of the extent of domain wall pinning, as manifested in changes in the spring constant α, decreasing with annealing and increasing with aging. The relaxation frequency is proportional to the extent of pinning, and initial permeability depends on the inverse.